The present invention relates to a flexible printed circuit board and its connecting method to another printed circuit board by soldering.
In JP Patent Publication No. H07-29/542, a method for connecting a flexible printed circuit board (hereinafter referred to as xe2x80x9cFPCBxe2x80x9d) to another printed circuit board (hereinafter referred to as xe2x80x9cPCBxe2x80x9d) by soldering is disclosed. FIG. 10 shows this connecting method. FPCB 100 has a through hole 105 as shown in FIG. 10. (In solder land part 7) of PCB 2, protrusive solder layer 8 is formed in advance, whereto the through hole 105 of FPCB 100 is engaged. By engaging the protrusive part of the solder layer 8 with the through hole 105, both FPCB 100 and PCB 2 are aligned with each other. In this state, heating solder layer 8 higher than its melting temperature enables FPCB 100 to connect with another PCB 2.
The above connecting method however, has left the following problems because the soldering area is very small. People could not determine from the appearance whether the entire solder land part had connected completely or not to the through whole part. Therefore, time was wasted by confirming the soldering completeness between boards. Further, the connecting intensity might not always be sufficient.
In a FPCB that has a through hole in the solder land part of the pattern layer between the cover layer and the base layer, the diameter of the through hole in the pattern layer is smaller than holes in the cover layer and the base layer. The solder land part in the FPCB provides the electrical connection part of the pattern layer, which corresponds with holes in the cover layer and base layer. The difference of the diameter of the holes, leads to an increased connecting area for soldering a FPCB to a PCB providing an accurate and strong soldering connection.